A Study of Urea-synthesizing Enzymes in Prenatal and Postnatal Human Liver

Abstract

Summary: The urea-synthesizing enzymes of human liver tissues, namely, carbamylphosphate synthetase (CPS, EC 2.7.2.2), ornithine transcarbamylase (OTC, EC 2.1.3.3), arginine synthetase system, argininosuccinase (ASase, EC 4.3.2.1), and arginase (EC 3.5.3.1) were measured between pre- and postnatal periods.

Specimens from 67 autopsied human livers obtained from fetuses, premature infants, newborn infants, infants, children, and adults were examined.

The mean activities of the enzymes showed an increased pattern for OTC and arginase at fetal life, whereas those of CPS, arginine synthetase system, and ASase of fetal livers showed no significant difference in each stage. Except for arginase, the other four enzyme activities were higher in the postnatal period than those in the fetal life. Arginase activities indicated maximal increase at a gestational age between 28 and 31 weeks and decreased in the postnatal life.

Speculation: The present study demonstrated that each of urea-synthesizing enzymes during fetal life developed independently. All five enzyme activities were present in 30% or more of the children even at a gestational age of between 12 and 19 weeks, and the enzyme activities of arginase increased with gestational age until birth. From the results, it may be possible to speculate that urea synthesis is always increasing during fetal periods.

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